The present invention relates to an enclosed lead storage battery usable as power source for portable electric devices. More particularly, the present invention relates to the improvements on the jacket enveloping electrode plate assembly and on the post extending out from the jacket.
Enclosed lead storage battery is widely used as a portable small-sized power source because of its electrolyte leak-proof structure. In such battery, the electrolyte is held against flowing by a separator such as glass mat so that it would not overflow the battery case or jacket.
In the conventional enclosed lead storage batteries, the electrode plate assembly consisting of a positive plate, a negative plate and a separator is housed in a box-like casing made of a synthetic resin material such as ABS resin (acrylonitrile-butadiene-styrene resin), and the casing is sealed by fastly bonding or welding a cover thereto.
In such conventional enclosed lead storage batteries, however, because of said structure, the shape and size of the battery case necessarily vary according to the battery voltage and capacity, so that the product batteries are varied in shape and size, which makes it difficult to mass-produce such batteries at low cost. Also, the production process involves many steps which defy mechanization such as insertion of plate assembly into the case, joining of cover and case, fitting of safety valve, etc., so that the productivity of such batteries is low resulting in high production cost.
As a solution to such problem, Japanese Patent Laid-Open No. 207558/84 proposes a method in which the battery case is made from a film- or sheet-formed synthetic resin such as polyethylene to envelop the plate assembly therein and the case is sealed by heat-sealing peripheral parts of the resins each other while simultaneously forming a safety valve. With such film or sheet of resin, however, it is difficult to meet the property requirements for battery case such as moisture permeability, oxygen permeability, acid resistance, tensile strength, burst strength, etc., and this has been a great obstacle to the commercialization of this type of batteries.
Also, in the batteries of such structure, it is required that each post is heat sealed with high reliability of sealing to the film- or sheet-formed synthetic resin constituting the jacket which envelops the plate assembly, with the end of said post extending out from the jacket. For such high-reliability of sealing, it is necessary to coat the thin ribbon-shaped or rod-like post with a polyethylene or polypropylene synthetic resin which can be heat sealed to the jacket, but there is yet available no method capable of commercial production of such posts at low cost.
Even if the post surface is directly coated with polyethylene or polypropylene synthetic resin, no strong adhesion is obtained between base lead or lead alloy and resin coating and the electrolyte would penetrate into the adhesion area between base post material and synthetic resin and leak out in a short time after coating due to capillarity of the electrolyte or corrosion of post. This has been another serious problem to be overcome for aquiring commercial reliability of this type of batteries.